Sheet acceleration and synchronization mechanism

ABSTRACT

A mechanism for accelerating sheet material to the circumferential speed of printing press cylinders or the like is accomplished by means of a rack having gear teeth which are mated with a pinion gear which is on the same shaft as the feed rollers for the sheets. The rack is driven by a cam which interacts with a cam follower on the rack so as to drive the rack in a sheetfeeding direction at an accelerated rate. The rack is then returned to its initial position by a return spring. The shaft which carries the rack drive cam also carries a cam which drives a cam follower for synchronizing the operation of a number of pinch rollers with the feed roller so that pinch rollers engage the sheet being fed only when the rack is moving in the sheetfeeding direction. The shaft which supports the pinion gear on one end also has a cam on its opposite end which controls another cam follower for synchronizing the operation of a stop mechanism for stopping the incoming sheets.

United States Patent Velan et al.

1 i SHEET ACCELERATION AND SYNCHRONIZATION MECHANISM [75] lnventors: George Michael Velan. Park Ridge;

Glenn Robert Peabody, Villa Park. both of 111.

[73] Assignee: Illinois Tool Works lnc., Chicago,

[22] Filed: Feb. 21, 1974 [2]] Appl No: 444,443

[52] US. Cl. 74/29; 74/55; 271/246 [511 int. Cl. l. Floh 19/04 [58] Field of Search .1 .74/55, 29, 30; 101/232; 271/246 [56] References Cited UNITED STATES PATENTS 1,160.185 11/1915 Mahlstcdt 271/246 2,437,345 3/1948 Bell l i v v 74/29 2,984,482 5/1961 Kist et al v l v l l l 271/246 3,427,888 2/1969 Rhcinliinden. 74/55 3,652,083 3/1972 Bosshardt .v 271/246 1 June 10, 1975 Primary Examiner-Samuel Scott Assistant Examiner-Wesley S. Ratliff, Jr.

i-trlorney, Agent, or Firm-Robert We Beart; Glenn W. Bowen 1 1 ABSTRACT A mechanism for accelerating sheet material to the circumferential speed of printing press cylinders or the like is accomplished by means of a rack having gear teeth which are mated with a pinion gear which is on the same shaft as the feed rollers for the sheets. The rack is driven by a cam which interacts with a cam follower on the rack so as to drive the rack in a sheetfeeding direction at an accelerated rate. The rack is then returned to its initial position by a return spring. The shaft which carries the rack drive cam also carries a cam which drives a cam follower for synchronizing the operation of a number of pinch rollers with the feed roller so that pinch rollers engage the sheet being fed only when the rack is moving in the sheet-feeding direction. The shaft which supports the pinion gear on one end also has a cam on its opposite end which controls another cam follower for synchronizing the oper ation of a stop mechanism for stopping the incoming sheets.

5 Claims, 4 Drawing Figures SHEET ACCELERATION AND SYNCIIRONIZATION MECHANISM BACKGROUND OF THE INVENTION Various mechanisms have been devised in order to accelerate incoming sheets into a printing press so that they obtain the circumferential speed of the printing press cylinders. However. these mechanisms have generally been unduly complex; and. moreover, they have required additional complicated mechanisms for synchronizing the operation of the pinch rollers and the sheet stop mechanism with the sheet acceleration mechanism.

It is therefore, an object of the present invention to provide a sheet acceleration mechanism in which a rack cam on a driven shaft is utilized to drive a cam fol lower on a rack gear having teeth which mesh with a pinion gear that is secured to a shaft that carries the feed roller whereby acceleration of the feed roller is achieved due to the acceleration of the rack gear, and wherein the pinch rollers are preferably brought into operative engagement with the feed roller by the interaction of another cam follower with a pinch roller cam that is also secured on the shaft that carries the rack cam.

It is an additional object of the present invention to provide a sheet acceleration mechanism in which a sheet stop mechanism is operatively controlled by a cam on one end of a shaft which carries a pinion gear on its opposite end which is driven by a rack gear that in turn is driven by another cam which interacts with a cam follower that is secured to the rack gear so that the pinion gear is accelerated and drives a feed roller which is also secured on the same shaft as the pinion gear.

It is a further object of the present invention to provide a sheet acceleration mechanism in which a pinion gear is secured to a shaft that also carries a feed roller and a rack gear meshes with the piniion gear and is driven by the interaction of a cam on a driven shaft and a cam follower on the rack gear so that the pinion gear will accelerate the feed roller to feeding sheets at an accelerated rate, wherein a spring is compressed when the rack gear is driven in the sheet-feeding direction and the energy of the spring is subsequently used to return the rack gear to its initial position.

Other objects and advantages of the present invention will be apparent to those skilled in the a.t from the disclosure found herein.

DESCRIPTION OF THE DRAWINGS The present invention is described by reference to the following drawings in which:

FIG. 1 is a plan view of the sheet acceleration and synchronizing mechanism of the present invention;

FIG. 2 is a partial side view of the mechanism of FIG. 1 taken along the lines 2-2 of FIG. 1;

FIG 3 is a partial side view of the opposite side of the frame taken along the lines 3-3 of FIG. 1 which shows the pinch roller cam in operating mechanism in detail; and

FIG 4 is a partial side view along the lines 4-4 of FIG. 1 which shows the sheet stop control mechanism in detail.

TECHNICAL DESCRIPTION OF THEKINVENTION The present invention is directed to a sheet insertion mechanism for a printing press in which the sheet to be inserted is accelerated to the circumferential speed of the printing press fed. to which it is ffed. Referring to FIG. I there is shown an input portion 8 of the printing press. In order to accelerate the incoming sheets to the circumferential speed of the printing press cylinders a rack and pinion gear assembly 14. which is located adjacent the lefthand frame member 10, is utilized.

The pinion gear I6 of the rack and pinion assembly 14 is mounted on a shaft 18. A feed roller 22 is also mounted on the shaft 18. The paper which is to be fed, represented by the sheet 24, is fed between a lower deflection plate 26 and an upper deflection plate 28 by the action of the feed roller 22 on the shaft I8 and a plurality of pinch rollers 30, which are located at spaced-apart locations between the frame members l0, 12. For simplicity of illustration only one pinch roller is shown in FIG. 1, but in practice a number of pinch rollers will be employed at the locations 31. The pinch rollers 30 are not driven rollers; and, therefore, the speed that the sheet 24 will be driven through the opening that is defined by the upper and lower sheet detectors 26, 28 when the pinch rollers 30 are brought to operative relationship adjacent to the feed roller 22 will be determined primarily by the rotational speed of the feed roller 22.

A rack gear 32 for accelerating the feed roller 22 is mounted so that it is guided in its movement along its longitudinal axis 34 by the guide 36 and a pair of eccentric idler rollers 38, 40 which roll against the rack gear 32 to restrain its motion along its longitudinal axis 34. In FIG. 2 when the rack gear 32 is being accelerated along its longitudinal axis 34 towards the lower righthand corner of FIG. 2 the paper feed roller 22 will be rotating in a counterclockwise direction so as to accelerate the sheet 24 through the detection plates 26, 28. The arrows that are shown adjacent the component parts of FIG. 2 are illustrative of the direction of motion of the associated elements when paper is being fed to the printing press.

A controlled rate of acceleration of the rack gear 32 is achieved by the configuration of the rack gear drive cam 42 which is secured to the shaft 45. The shaft 45 is driven by the gear train of the press (not shown) at a substantially constant rotational speed. A cam follower 44, which is secured to the rack gear 32, traverses the surface of the cam 42 from the high area 48 of the cam to the low or dwell area 46 of the cam 42. The cam follower 44 will thus be driven downwardly thereby driving the rack gear 32 downwardly so as to compress a spring 50 which surrounds a rod 52 that extends from the lower end of the rack gear 32, which the cam follower 44 engages the area 48 of the cam 42. The spring 50 is retained between a shoulder 54 on the lower end of the rack gear 32 and a spring retaining block 56.

When the printing press is in operation sheets are constantly being fed to it. These sheets must be stopped at the input portion 8 of the press so that they can be acted on by the feed roller 22 and the pinch rollers 30, and thereby accelerated to the printing press at the appropriate speed. In order to achieve this it is necessary to synchronize the operation of the sheet stop members 58 and the pinch rollers 30 with the rack and pinion assembly 14. The pinch rollers 30 also must be in an operative position adjacent the feed roller 22 only when the roller 22 is being accelerated in a counterclockwise, sheet-feeding direction.

FIG. 2 shows the relative position of the acceleration mechanism of the present invention when the cam 42 engaging the dwell area 46 of the cam follower 44. The dwell area 46 of the cam 42 lies between the 264 line and the of the cam 42 in FIG. 2. When the cam follower 44 is in engagement with the low dwell portion 46 of the cam 42 the rack 32 will remain relatively stationary along the longitudinal axis 34 since the radius of the section 46 with respect to the center of the shaft 45 is relatively constantv While the rack gear 32 is in its stationary position the stop members 58 will extend upwardly in the openings 59. The pinnch rollers 30 are placed so that they have a stop member 58 on each side of them. During the time that the cam follower 44 is in contact with the low dwell portion 46 of the cam 42 the pinch rollers 30 will be lifted away from the feed roller 22 so that feeding nips will not be formed between the feed roller 22 and the pinch rollers 30.

The periphery of the cam 42 is located between the 0 line and the 81 line is the area over which the acceleration of the sheet 24 occurs. Following the acceleration of the paper over this area the paper is fed at a constant speed as the cam follower 44 traverses the periphery of the cam 42 over the surface of the cam between the 81 and the l04 line which has a constant radius. The speed of the paper is maintained constant over this area of the cycle so that a critical lift-off time is not needed for the pinch rollers 30. This constant speed portion also tends to prevent buckling of the paper or dragging by the grippers which could result in marring the sheet. After the cam follower 44 has traversed the paper feed acceleration portion 48 and the constant speed portion 49 of the cam 42 the area of the cam between the l04 line and the 264 line is the roll return section of the cam. The roll return portion of the cycle is to allow for a long enough rack return time so that a sheet passing through the press will not interfere with the next incoming sheet.

As the cam 42 rotates in a counterclockwise direction the rack gear 32 remains stationary while the cam follower traverses the dwell area 46. When the cam follower travels up the ramp 53 onto the high portion 48 of the cam 42 the cam follower 44 and the rack gear 32 are driven downwardly relatively rapidly thereby compressing the spring 50. Due to the abrupt increase in radius between the dwell area 46 and the high area 48 the rack gear 32 will be accelerated downwardly at a controlled rate. This rapid downward acceleration of the rack gear 32 causes a counterclockwise accelera tion of the pinion gear 16; and, consequently, of the feed roller 22. The pinch rollers 30 are brought into operative position with respect to the feed roller 22 at approximately the 12 line and they maintain this position for approximately 70 or until the cam follower 44 is just passed slightly past the 81 line. Since the radius of the cam 42 between the 81 and the 104 line is relatively constant the time that the pinch rollers 30 are lifted from their nip forming position with respect to the feed roller 22 is not critical. Past the l04 line the pinch rollers 30 are displaced upwardly from their operative position as the radius of the cam 42 decreases steadily and the compressive force on the spring 50 is thereby relieved until the cam 44 reaches the constant radius low dwell area 46.

FIGS. 3 and 4 show the elements of the invention that are located adjacent to the righthand frame member 12. In viewing the press shown in FIG. I along the lines 33 both the pinch roller operating mechanism and the sheet stop operating mechanism could be seen. However, for clarity of presentation the sheet stop operating mechanism is shown in a separate view in FIG. 4, which is taken along the lines 44 of FIG. 1, rather than in FIG. 3.

As previously mentioned, FIG. 2 shows the position of the rack and pinion assembly 14 when the cam gear 42 is positioned so that cam follower 44 is in engagement with the low dwell area 46 of the cam 42. When the cam follower 44 and the cam 42 are located as shown in FIG. 2 the sheet stop members 58 will be positioned in their upward or operative positions with respect to the feed roller 22. FIG. 3 shows the relative relationship of the pinch rollers 30 and the feed roller 22 when the cam follower 44 is in engagement with the sheets acceleration area 48 of the cam 42 and a sheet 24 is being accelerated into the printing press.

The shaft 45 which carries the rack cam 32 has a gear (not shown) on it which is coupled to the main gear drive train so that the shaft 45 is driven at a substantially constant rotational velocity by the main drive for the printing press. The righthand side of the shaft 45 extends through the frame I2 and carries a pinch roller cam 82 on its outer end. The pinch roller cam 82 is po sitioned so that it engages a cam follower 84 which is secured to a pinch roller lever arm 86. The pinch roller lever arm 86 has a generally Z-shaped configuration and the cam roller 84 is positioned adjacent to the bottom leg 88 of the arm 86. The cam follower 84 is c0nfigurated such that the pinch rollers 30 will be positioned in operative engagement with the roller 22 only when the cam follower 84 is in engagement with the high area 90 of the cam 82. The high" area 90 of the cam 82 extends for approximately around the circumference of the cam 82, and the cam follower 84 will be in contact with the area while the cam follower 44 is traversing over the periphery of the cam 42 between approximately the 12 and the 82 portion of the cam 42. Thus the pinch rollers 30 will be lowered so as to be adjacent the feed rollers 22 to form a number of sheet engaging nips along the length of the feed roller 22 when the rack cam 32 is being accelerated downwardly by the interaction of the cam follower 44 and the cam 42.

The upper end of the pinch roller lever arm 86 has a flanged bearing 92 which surrounds the shaft 94 which allows the lever arm 96 to rotate on the bearing 92 above the shaft 94. The shaft 94 carries the pinch roller holders 100. The bearing 92 is secured to the shaft 94 by a threaded paper pin 97 and a nut 98. In order to return the lever arm 96 to its initial position a return spring 106 is provided which surrounds a rod 107 and extends between an extension leg 102 of the leg 88 and a spring post 104. The rod 107 which is threaded into the spring post 104 and extends through an aperture 109 in the extension leg 102 so that it may slide in the aperture 109 relative to the leg 102.

The cam follower 84 engages the low area I08 of the cam 82 the spring 106 is allowed to expand. thereby rotating the lever arm 86 with respect in a counterclockwise direction with respect to the shaft 94 which lifts the pinch rollers 30 away from the feed roller 22. The extension 102 may carry a small L-shaped finger 108 at its outer end for engaging a roller 110 which is mounted on the end of an operating lever 112 of an electrical switch 114. The switch 114 may thereby be used to provide an indication to the electrical control circuitry of the press each time that the sheet is fed into the press and the pinch rollers are lowered into their opposite position.

As previously mentioned, location of the pinch rollers 30 relative to the feed roller 22 is controlled by the position of the lever arm 86, since rotation of the lever arm 86 causes a similar rotation of the shaft 94 to which it is secured. This is achieved because the pinch rollers 30 are mounted in pinch roller holders 110 which are also mounted onto the shaft 94. The pinch roller holders 110 consist ofa pair of spaced-apart arms 117, 119 which receive the opposite ends of an axle 121 for its respective pinch roller 30. The pinch roller holders 110 are secured to the shaft 94 by the bolts 122, or other suitable securing means and, therefore, rotation of the shaft 94 will cause displacement of the pinch rollers 30 from the feed roller 22 when the shaft 94 is rotated in a counterclockwise direction, as shown in FIG. 3. Alternately, the pinch rollers 30 will be moved into their operative position with respect to the feed roller 22 when the shaft 94 is rotated in a clockwise direction as shown in FIG. 3.

Also shown in FIG. 4, the sheet stop members 58 are secured to one end ofa sheet stop carrier 64. The other end of the carrier 64 has a bracket 66 which supports a cam follower 68 and a spring post 70. A return spring 72 is coupled between the spring post 70 and a fixed spring post 74. The shaft 18, which carries the pinion gear 16 and the feed roller 22 at its opposite end near the frame member 10, also carries a cam 78 on its end adjacent the frame member 12 which has a small detent 80 in its outer periphery. When the cam follower 68 is on the high portion of the cam 78 the carrier 64 will be rotated slightly in a clockwise direction, as viewed in FIG. 4, thereby withdrawing the edges 59 of the stop members 58 below the level of the lower sheet deflectors 26 so as to allow passage of the incoming sheet 24. When the stop members 58 are displaced downwardly the spring 72 is stretched so as to provide a source of energy for subsequently returning the stop members 58 to their operative positions.

The upper edges 59 of the stop member 58 remains below the lower sheet deflector 26 until the cam 78 rotates sufficiently so that the cam follower 68 can drop into the detent 80 as a result of the force supplied by the spring 72. The detent 80 on the cam 78 is located so that the stop members will project upwardly into the slot 62 so as to stop the incoming sheet prior to the time the feed roller 22 begins to be accelerated by the rack pinion assembly 14. The cam follower 68 will be forced into the detent 80 at substantially the same time that the cam follower 44 engages the periphery of the cam 42 at the 264 line of FIG. 2. Since there is no motion of the rack cam 32 while the cam follower 44 is traversing the low dwell area 47 of the cam 42 the pinion gear 16 of the shaft 18 will not be rotated during this time. Therefore, the cam follower 68 will remain in the detent 80 until the cam follower 44 reaches approxi mately the 0 line of the cam 42, at which time the rack gear 32 will begin to be accelerated, thereby initiating rotation of the shaft 18 of the pinion gear 16. Thus, the cam follower 68 will be forced out of the detent 80 shortly after the cam 44 passes 0 line on the periphery of the cam 42.

While a particular embodiment has been shown and described, other embodiments within the spirit and scope of the present invention which are embraced within the claims will be apparent to those skilled in the art.

The invention is claimed as follows:

1. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh with said rack gear. a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft. drive means for driving said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the direction along its longitudinal axis which accelerates said feed roller in its paper-feeding rotational direction, sheet stop means, sheet stop carrier means for carrying said sheet stop means comprising a sheet stop cam follower and a sheet stop cam on said first shaft for actuating and deactuating said sheet stop means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said first shaft, said pinion gear being secured on the end of said first shaft adjacent said flrst frame member while said sheet stop cam is secured on the end of said first shaft adjacent said second frame member.

2. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh with said rack gear, a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft, drive means for driv ing said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the direction along its longitudinal axis which accelerates said feed roller in its paper-feeding rotational direction, a pinch roller means constructed to be selectively operatively positioned with respect to said feed roller, pinch roller carrier means on said pinch roller means comprising a pinch roller cam follower and a pinch roller cam on said second shaft for actuating and deactuating said pinch roller means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said second shaft, said rack drive cam being secured on the end of said second shaft adjacent said first frame member and said pinch roller cam being secured on the end of said second shaft adjacent said second frame member.

3. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh with said rack gear, a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft, drive means for driving said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the direction along its longitudinal axis which accelerates said feed roller in its paper-feeding rotational direction, sheet stop means, sheet stop carrier means for carrying said sheet stop means comprising a sheet stop cam follower and a sheet stop cam on said first shaft for actuating and deactuating said sheet stop means at predetermined times, a pinch roller means constructed to be selectively operatively positioned with respect to said feed roller, pinch roller carrier means on said pinch roller means comprising a pinch roller cam follower and a pinch roller cam on said second shaft for actuating and deactuating said pinch roller means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said first shaft, said pinion gear being secured on the end of said first shaft adjacent said first frame member while said sheet stop cam is secured on the end of said first shaft adjacent said second frame member.

4. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh with said rack gear, a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft, drive means for driving said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the direction along its longitudinal axis which accelerates said feed roller in its paper-feeding rotational direction, sheet stop means, sheet stop carrier means for carrying said sheet stop means comprising a sheet stop cam follower and a sheet stop cam on said first shaft for actuating and deactuating said sheet stop means at predetermined times, a pinch roller means constructed to be selectively operatively positioned with respect to said feed roller, pinch roller carrier means on said pinch roller means comprising a pinch roller cam follower and a pinch roller cam on said second shaft for actuating and deactuating said pinch roller means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said second shaft, said rack drive cam being secured on the end of said second shaft adjacent said first frame member while said pinch roller cam is secured on the end of said second shaft adjacent said second frame member.

5. A sheet feeding mechanism as claimed in claim 4 wherein said pinion gear is secured on the end of said first shaft adjacent said first frame member while said sheet stop cam is secured on the end of said first shaft adjacent said second frame member. 

1. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh with said rack gear, a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft, drive means for driving said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the direction along its longitudinal axis which Accelerates said feed roller in its paper-feeding rotational direction, sheet stop means, sheet stop carrier means for carrying said sheet stop means comprising a sheet stop cam follower and a sheet stop cam on said first shaft for actuating and deactuating said sheet stop means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said first shaft, said pinion gear being secured on the end of said first shaft adjacent said first frame member while said sheet stop cam is secured on the end of said first shaft adjacent said second frame member.
 2. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh with said rack gear, a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft, drive means for driving said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the direction along its longitudinal axis which accelerates said feed roller in its paper-feeding rotational direction, a pinch roller means constructed to be selectively operatively positioned with respect to said feed roller, pinch roller carrier means on said pinch roller means comprising a pinch roller cam follower and a pinch roller cam on said second shaft for actuating and deactuating said pinch roller means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said second shaft, said rack drive cam being secured on the end of said second shaft adjacent said first frame member and said pinch roller cam being secured on the end of said second shaft adjacent said second frame member.
 3. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh with said rack gear, a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft, drive means for driving said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the direction along its longitudinal axis which accelerates said feed roller in its paper-feeding rotational direction, sheet stop means, sheet stop carrier means for carrying said sheet stop means comprising a sheet stop cam follower and a sheet stop cam on said first shaft for actuating and deactuating said sheet stop means at predetermined times, a pinch roller means constructed to be selectively operatively positioned with respect to said feed roller, pinch roller carrier means on said pinch roller means comprising a pinch roller cam follower and a pinch roller cam on said second shaft for actuating and deactuating said pinch roller means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said first shaft, said pinion gear being secured on the end of said first shaft adjacent said first frame member while said sheet stop cam is secured on the end of said first shaft adjacent said second frame member.
 4. A sheet feeding mechanism comprising a first shaft, a rack gear having a longitudinal axis, a pinion gear on said first shaft in mesh will said rack gear, a feed roller on said first shaft for feeding said sheets, a rotationally driven second shaft, drive means for driving said rack gear along its longitudinal axis, said drive means comprising a cam follower coupled to said rack gear and a rack drive cam on said second shaft which has a cam surface that interacts with said cam follower and has a curvature such that the rack gear is accelerated in the diRection along its longitudinal axis which accelerates said feed roller in its paper-feeding rotational direction, sheet stop means, sheet stop carrier means for carrying said sheet stop means comprising a sheet stop cam follower and a sheet stop cam on said first shaft for actuating and deactuating said sheet stop means at predetermined times, a pinch roller means constructed to be selectively operatively positioned with respect to said feed roller, pinch roller carrier means on said pinch roller means comprising a pinch roller cam follower and a pinch roller cam on said second shaft for actuating and deactuating said pinch roller means at predetermined times, and first and second spaced apart frame members each of which support one of the opposite ends of said second shaft, said rack drive cam being secured on the end of said second shaft adjacent said first frame member while said pinch roller cam is secured on the end of said second shaft adjacent said second frame member.
 5. A sheet feeding mechanism as claimed in claim 4 wherein said pinion gear is secured on the end of said first shaft adjacent said first frame member while said sheet stop cam is secured on the end of said first shaft adjacent said second frame member. 